Chains and toothed belts are typically used to drive the camshafts of internal combustion engines. These types of endless bands are used because they maintain the timing of the camshaft relative to the crankshaft. Guides or pulleys are used to take up slack in the endless band. If there is too much slack, the endless band can jump a pulley tooth and loose correct timing. The belt can also thrash, causing noise and wear. If the endless band is to taut the endless band and guides will wear out quickly and may break. In all mass production engines, the chain guides or pulleys are positioned for providing a slackless belt that is nether too loose or too taut.
Internal combustion engine efficiency can be improved by varying the compression ratio of the engine. One method of varying the compression ratio of the engine is to vary the distance between the cylinder head of the engine and the crankshaft of the engine. A problem with these variable compression ratio engines, however, is that the center distance changes between the drive pulley on the crankshaft and the driven pulley on the camshaft. When the center distance between the drive pulley and driven pulley is reduced, the endless band becomes too slack and the drive pulley no longer turns the belt or chain. A method is needed for maintaining a slackless endless band when the center distance changes between the drive pulley on the crankshaft and the driven pulley on the camshaft.
A variable compression ratio engines having an adjustable distance between the cylinder head and crankshaft is taught by Hans Dranglel et al. of Saab Automobile Powertrain AB in Society of Automotive Engineers technical paper “The Variable Compression (SVC) and the Combustion Control (SCC)—Two Ways to Improve Fuel Economy and Still Comply with World-Wide Emission Requirements” SAE paper No. 2002-01-0996, March 2002, and in Automotive Engineering International magazine pages 54-57, April 2001. The variable compression ratio engine is also taught by Gillbrand et al. in U.S. Pat. No. 5,611,301. Referring now to FIG. 2 of U.S. Pat. No. 5,611,301, the Saab engine includes a lower crankcase section (13) and a cylinder section or cylinder jug (11) connected to the crankcase with a pivot shaft (19) on a first side of the crankcase, and control shaft or eccentric shaft (44) and rods (41) on the other side of crankcase (13). Cylinder head (26) mounted on cylinder section or cylinder jug (11) is referred to as a monohead in Society of Automotive Engineer publications. The variable compression ratio mechanism taught by Saab enables the monohead (11, 26) to pivot or tilt relative to the crankcase (13) of the engine about the pivot shaft (19).
The Saab variable compression ratio engine has a variable center distance between the drive pulley mounted on the crankshaft (14) and the driven pulley mounted on the camshaft (32). Saab teaches use of a two stage endless band system where a pair of middle pulleys rigidly attached to one another for rotation at the same speed and in the same direction is mounted on or coaxially with the pivot shaft (19). A first endless band connects the crankshaft drive pulley to the first middle pulley, and a second endless band connects the second middle pulley to the camshaft (32). The system operates at various compression ratio settings because the center distance between the first middle pulley mounted on pivot shaft (19) and crankshaft (14) never changes, and the distance between the second middle pulley mounted on pivot shaft (19) and the camshaft (32) never changes. A problem with the Saab system for driving the camshaft (32) from the crankshaft (14) is that it increases engine length.
Another variable compression ratio engine (2) having a single control shaft (20) per cylinder head (16) is taught by Mendler in International Application Number PCT/US2013/000023. Mendler does not show or teach a method for taking up slack in the camshaft drive belt when the center distance between the drive pulley (11) on the crankshaft (10) and the driven pulley (15) on the camshaft (13) is varied.
Another variable compression ratio engines having an adjustable distance between the cylinder head and crankshaft is taught by Howard C. Vivian in U.S. Pat. No. 4,174,683. The Vivian engine includes a crankcase or crankcase sub assembly (12), an upper cylinder head (10) and a cylinder block or cylinder jug (11). Upper cylinder head (10) and cylinder block or cylinder jug (11) are combined forming a monohead (10 and 11). Cylinder block or cylinder jug (11) is connected to the crankcase (12) with a pair of eccentric shafts or control shafts (13 and 14). A sprocket or drive pulley (44) is mounted on crankshaft (15) for driving toothed belt (45), and the tooth belt (45) drives sprocket or driven pulley (46) mounted on camshaft (29). FIG. 4 and column 7 of U.S. Pat. No. 4,174,683 describe “a pair of slack takeup idlers (47, 49) cooperating with an adjustable tensioning idler (48) all supported on a mounting (50) attached to one end of the cylinder block (11).” The Vivian patent does not effectively teach how the idlers (47) and (49) would be moved to take up slack. A rocker arm attached to cylinder jug (11) appears to be shown in FIG. 10, but it is not mentioned or described in the specification of U.S. Pat. No. 4,174,683.
Another variable compression ratio engines having an adjustable distance between the cylinder head and crankshaft is taught by Kodama of Toyota in U.S. Pat. No. 8,671,894, and Akihisa et al. in U.S. Pat. No. 7,047,917. The Kodama engine includes a lower crankcase (22), an upper cylinder head (3) and a cylinder block or cylinder jug (2). Cylinder head (3) and cylinder block (2) form a monohead. The Kodama engine also includes a crankshaft (4) having a crank shaft gear (8) for driving camshafts (6 and 7), a driven camshaft gear or first driven pulley (13), and a chain or belt (14) for driving the first pulley (13). Cylinder block or cylinder jug (2) is connected to the crankcase (22) with a pair of main shafts or eccentric shafts or control shafts (24) located on both sides of crankcase (22). FIG. 1 and column 10 of U.S. Pat. No. 8,671,894 teaches use of a rotation transmission shaft (5) to accommodate change of the center distance between the crankshaft gear (8) mounted on the crankshaft (4) and the camshaft gear or driven pulley (13) mounted on camshaft (7). A first problem with the system taught by Kodama for driving camshaft (7) with crankshaft (4) is the cost and complexity of rotation transmission shaft assembly (5). Another problem with the Kodama system for driving the camshaft (7) from the crankshaft (4) is that it increases engine length.
Accordingly, an objective of the present invention is to provide a slackless endless band system for a variable compression ratio engine having a variable center distance between the drive pulley mounted on the crankshaft and the driven pulley mounted on the camshaft. The system should provide slackless operation of the endless band at two or more compression ratio values. The system should also have a small size, and in particular, not increase engine length. The endless band system for the variable compression ratio engine should also provide durability, noise, system cost and frictional loss values that are similar or no worse than current production endless band drive systems for internal combustion engines that do not have a variable compression ratio.